Masses can be a capella, for the human voice alone, or they can be accompanied by instrumental obbligatos[?] up to and including a full orchestra. Generally, for a composition to be a full Mass, it must contain the following six sections, which together constitute the "ordinary" of the Mass:

I. Kyrie

The text here is simply: Kyrie eleison; Christe eleison; Kyrie eleison (Κυριε ελεησον; Χριστε ελεησον; Κυριε ελεησον). This is Greek for "Lord have mercy on us; Christ, have mercy on us; Lord, have mercy on us."

II. Gloria

This is a celebratory passage praising God and Christ, which sets the following text:

Glory to God in the highest, and on earth peace to men of good will. We praise Thee, we bless Thee, we adore Thee, we glorify Thee, we give thanks to Thee for Thy great glory, Lord God, heavenly King, almighty God the Father.

Lord Jesus Christ, only begotten Son, Lamb of God, Son of the Father, Thou who takes away the sins of the world, have mercy on us; Thou who takes away the sins of the world, hear our prayers. Thou who sittest at the right hand of the Father, have mercy upon us.

For Thou art the only Holy One, the only Lord, the only Most High, Jesus Christ, with the Holy Spirit in the glory of God the Father, Amen.

III. Credo

The longest text of the Mass, this is a setting in Latin of the Nicene Creed.

IV. Sanctus

This is a doxology praising the Trinity which begins with the words Sanctus, Sanctus, Sanctus, Domine Deus Sabaoth; pleni sunt coeli et terra gloria tua (Holy, Holy, Holy, Lord God of Hosts; Heaven and earth are full of thy glory). There is also a section that begins with the words Hosanna in excelsis, "Hosanna in the highest."

V. Benedictus

This is a setting of the Latin words Benedictus qui venit in nomine Domini. (Blessed is he who comes in the name of the Lord).

After this is sung, the Hosanna is usually repeated.

VI. Agnus Dei

A setting of the Latin phrases,

Agnus Dei, qui tollis peccata mundi,

miserere nobis /

dona nobis pacem.

(Lamb of God, who takes away the sins of the world, have mercy upon us / give us peace.)

In a liturgical Mass, there are other sections that may be sung, often in Gregorian chant. These sections change with the day and season according to the Church calendar, and are usually not set to music by a composer who wishes to write a Mass. They can, and have been made the subject of motets and other musical compositions, however.

These sections of the Mass as a musical composition have been standard since the Middle Ages; the very earliest Masses may include other parts, and omit some of the standard ones. The first Mass we know of whose composer can be identified was the Mass of Our Lady by Guillaume de Machaut. Many other composers wrote Masses, including Johann Sebastian Bach, who was not a Roman Catholic. Perhaps the greatest composer of church music ever was Giovanni Pierluigi da Palestrina, whose Mass for Pope Marcellus is credited with saving polyphony from the censure of the Council of Trent.